1. Field of the Invention
The present invention relates to an organic light emitting display which includes an organic light emitting layer between a pair of electrodes and emits light from the organic light emitting layer by applying electric fields to the light emitting layer using the pair of the electrodes, and more particularly to an organic light emitting display which acquires long lifetime and high reliability by preventing deterioration of light emitting area efficiency of organic light emitting elements caused by heat generated from the organic light emitting layer which constitutes the light emitting area.
2. Description of Related Arts
Currently, a flat-panel-type display such as a liquid crystal display (LCD), a plasma display (PDP), a field-emission-type display (FED), an organic light emitting display (OLED) has been put to practical use or under development for practical use. Among these displays, the organic light emitting display is a highly expected display as a typical thin and light-weight self-light-emission-type display. The organic light emitting display can be divided into so-called bottom emission type and top emission type.
According to the bottom-emission-type organic light emitting display, organic light emitting elements have a light emitting mechanism produced by sequentially laminating, on an insulating substrate which is preferably a glass substrate, a transparent conductive thin layer formed by ITO (In—Tin (Sn)—O) or IZO (In—Zn—O) or the like as a first electrode or one electrode, an organic light emitting layer (also referred to as organic multilayer) which emits light when electric fields are applied, and a reflective metal electrode as a second electrode or the other electrode. A number of the organic light emitting elements thus produced are arranged in matrix, and the resultant laminating structure is covered by another substrate also referred to as encapsulating can so that the light emitting structure can be isolated from the outside atmosphere.
When electric fields are applied between the transparent electrode set as anode and the metal electrode set as cathode, for example, carriers (electrons and holes) are injected into the organic light emitting layer and thus light is emitted from the organic light emitting layer. The emitted light is released through the glass substrate to the outside.
In the top-emission-type organic light emitting display, electric fields are applied between a reflective metal electrode as one electrode and a transparent electrode formed by ITO or the like as the other electrode to cause emission of light from the organic light emitting layer. The emitted light is released from the other electrode. The top-emission-type display uses a transparent plate, preferably a glass plate, as the encapsulating can similar to that of the bottom-emission-type display.
FIGS. 5A and 5B schematically illustrate a known structure example of an organic light emitting display. FIG. 5A is a plan view showing the entire structure of a main part, in which peripheral semiconductor elements, organic electroluminescence sections and the like disposed on the lower surface of a cathode layer are shown on the upper surface thereof for the sake of simplification. FIG. 5B is an enlarged cross-sectional view showing a pixel and its vicinity taken along a line A-B in FIG. 5A.
The organic light emitting display shown in FIG. 5 is of active matrix type, and includes a thin-film transistor TFT on the main surface (inner surface) of a light-transmissive main substrate SUB1 which is preferably glass. Organic light emitting elements EL are produced by inserting an organic light emitting layer OLE between first electrodes ADs (anodes in this example) driven by the thin-film transistor TFT and a second electrode (cathode in this example) CD. The thin-film transistor TFT is constituted by a polysilicone semiconductor layer PSI, a gate insulating layer IS1, a gate line (gate electrode) GL, a source drain electrode SD, and an intermediate insulating layer IS2.
Each of the anodes ADs as pixel electrodes is constituted by a transparent conductive layer (ITO) formed on the upper surface of a passivation layer PSV, and is electrically connected with the source drain electrode SD at a contact hole CH1 provided on the passivation layer PSV. The organic light emitting layer OLE is formed on a concave surrounded by a bank BNK produced by an insulating layer applied onto the anode AD by deposition, ink-jet method or other application methods.
The cathode CD formed by a conductive overall layer such as aluminum thin layer and chrome thin layer covers the organic light emitting layer OLE and the bank BNK. One end of the cathode CD is electrically connected with a cathode line CDL provided on the intermediate layer IS2 at a contact hole CH2 formed on the passivation layer PSV out of the pixel area.
A display area AR is produced by arranging a number of pixels shown in FIG. 5B in matrix in a major part of the center of the main substrate SUB1. Scanning drive circuits (gate drivers) GDR1 and GDR2 are provided on the left and right sides of the display area AR, and not-shown respective gate lines extending from the gate driver GDR1 and the gate driver GDR2 are alternately disposed. A data drive circuit (drain driver) DDR is equipped below the display area AR, and not-shown drain lines as data lines cross the respective gate lines.
A current supply bus CSLB is provided above the display area AR, and current supply lines CSL extend from the current supply bus CSLB. In this structure, one pixel is provided within an area surrounded by the respective gate lines, the drain lines, and the current supply lines CSL. The cathode CD covers the display area AR, the respective gate drivers GDR1 and GDR2, and the drain driver DDR inside a seal member SL. A contact area CTH connects the cathode CD with the cathode line CDL provided on the lower surface of the main substrate SUB1.
Also provided are signal supply lines GL1 and GL2 of the gate driver GDR1, signal supply lines GL3 and GL4 of the gate driver GR2, a signal supply line DL1 of the drain driver DDR, an electrode line SDL of the source drain electrode SD, and an input terminal TM connecting the respective signal supply lines GL1, GL2, GL3, GL4, DL1, the cathode line CDL, the anode line, and other lines to the external circuits.
The organic light emitting display in this example is a so-called bottom-emission-type display. Light L emitted from pixel openings of the organic light emitting layer OLE is released through the surface of the main substrate SUB1 to the outside in the direction shown by an arrow. Thus, the cathode CD has light reflection capability. An encapsulating glass substrate SUB2 also referred to as encapsulation can is affixed to the main surface of the main substrate SUB1 via the seal member SL so as to encapsulate the inside of the seal extending around the not-shown circumferential area into a vacuum condition.
According to the organic light emitting display having this structure, when carriers are injected into the organic light emitting layer OLE of the light emission mechanism in accordance with electric fields applied between the anode AD and the cathode CD, the organic light emitting elements EL emit light. In this case, not all carriers thus injected are used for light emission, but a part of those generates heat and applies heat to the light emission mechanism. Generated heat generally deteriorates the light emission characteristic of the material of the organic light emitting layer OLE constituting the light emission mechanism, and shortens its lifetime. It is therefore necessary to eliminate this heat generation.
To cope with the problem of heat generation, a structure disclosed in Japanese Patent Laid-Open No. 22891/2003 enhances radiation of heat by enlarging the surface area of a cathode. A structure shown in Japanese Patent Laid-Open No. 47458/2004 improves radiation of heat by interposing a thermal conductive spacer between a cathode and an encapsulating substrate and forming metal coating layer on the surface of the encapsulating substrate. A structure described in Japanese Patent Laid-Open No. 93574/2002 attains greater radiation of heat by injecting highly thermal-conductive liquid between a cathode and an encapsulating substrate. A structure explained in Japanese Patent Laid-Open No. 237063/2001 offers greater radiation of heat by providing a radiation layer having holes corresponding to the shapes of respective pixels on the viewing surface of a substrate.